The use of threaded nuts to tighten onto bolts is well known. In a conventional fashion nuts are tightened by threaded rotation in one direction, and loosened by threaded rotation in the other direction.
In some environments conventional loosening of nuts becomes difficult or impossible. Over time a nut can bind to a bolt, or have corrosion or other damage done to the thread of the nut and/or bolt, particularly to the exposed section of the thread, which prevents nut removal. Frequently it becomes necessary to cut the nut away, mechanically or by use of an oxyacetylene torch or similar. Such an action is time consuming, and can raise significant safety concerns.
In other situations the nut may loosen to an extent, but there may be sufficient friction between nut and bolt for applied rotation to the nut to cause rotation of the nut-and-bolt together. It can be difficult or time consuming to restrain a head of the bolt while removing the nut. Indeed, in some situations there may be intervening structures between the bolt head and the nut, meaning that removal of the nut becomes a two-person operation, requiring coordination and sometimes the erection of access platforms. To avoid this situation, many industrial environments dictate cutting of a nut as standard practice.
In addition to man-power and safety concerns, other adverse consequences can arise from the requirement to cut nuts using oxyacetylene torches. It is often desirable to use anti-rotation devices, such as a polymer insert (a ‘nyloc’) within a nut. In environments where oxyacetylene cutting of nuts is required, the use of such inserts is banned, and other solutions for anti-rotation problems must be found.
Segmented nuts, being nuts formed in two or three circumferentially arranged pieces, are known. In one common type, the pieces are connected by thin webs. This allows a segmented nut to function as a normal nut during fastening, but allows it to be readily broken into pieces for quick removal. This is considered particularly advantageous in adverse environment conditions such as those described above.
This type of segmented nut has limitations. In particular, it can be difficult to achieve an appropriate balance between the strength required to maintain the nut in position in use, and the ease with which the webs can be broken for removal.
Another known type of segmented nut is formed from circumferentially arranged pieces held together by a surrounding collar. In this nut, the collar contains clamping screws which apply a radial force to the nut segments, forcing them together. Release of the clamping screws allows radial movement of the nut pieces away from the bolt. The threads of the clamping screws in these bolts can suffer the same problems as the nut threads, being liable to corrode or otherwise seize within the collar. Additionally, they are necessarily considerably smaller than the nut and thus require an additional degree of dexterity and finesse to remove. This is not always convenient or indeed possible.
In an alternative design, attempts have been made to form a segmented nut from circumferentially arranged pieces held together by an axially moveable collar. In such a design, the idea is that the collar is slid in an axial direction in order to release the nut pieces. Such nuts are highly problematic, in use. It can be difficult to achieve sufficient purchase on the sleeve in order to provide a suitable axial force. In corrosive environments the necessary axial force can be considerable, and as will be appreciated applying axial forces to an annular surface in a confined space can be difficult if not impossible.
The present invention seeks to address some of the limitations of prior segmented nuts.